"The Voltage Tweak model from ASUS is something we've heard about for a while now. The idea behind it is that ASUS gives the user even more control of the card when it comes to overclocking. Not only do you have the ability to overclock the standard clocks like memory and core, but you also have the ability to adjust the voltage.
You may be wondering what this exactly means; it gives you the ability to adjust the voltage to higher levels which in turn gives you the ability to run the card at even higher speeds, much like you do with a CPU where adding more voltage gives you the ability to obtain higher clock speeds."